PO means by mouth. I haven't used fluconazole, so I'm not sure how well diluting it works. It apparently doesn't dissolve in water very well. If it floats or something, it could possibly be more difficult to give. I usually don't dilute unless the amount is so small that it's hard to manage.
Another article I saw mentioned that it may gain immunity to Nystatin and certain other treatments over time, but I couldn't find a copy of the source for more details. I suspect they were using low dosages. The fluconazole should help, it just may not totally eradicate it, according to the...
C. Glabrata can be resistant to fluconazole. It's been fairly well studied. Here's a source about treatment options in humans:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC88907/?report=reader